An electric power steering apparatus for applying a steering assist force to a steering mechanism of an automobile by a rotating force of a motor transmits a driving force of the motor by a transmitting mechanism such as a gear or a belt through a reduction gear to apply the steering assist force to a steering shaft or a rack shaft. An example of a structure of such an electric power steering apparatus is shown in FIG. 1 and will be described.
A shaft 102 of a steering wheel 101 is coupled to tie rods 106 of steered wheels through a reduction gear 103, universal joints 104a and 104b, and a pinion rack mechanism 105. The shaft 102 is provided with a torque sensor 107 for detecting steering torque of the steering wheel 101, and a motor 108 for assisting a steering force of the steering wheel 101 is coupled to the shaft 102 through the reduction gear 103. The motor control of the electric power steering apparatus is controlled by a control unit 109 by inputting a torque value detected by the torque sensor 107, a vehicle speed detected by a vehicle speed sensor (not shown), a rotation angle of the motor detected by a Hall sensor 110, and the like to the control unit 109. The control unit 109 is mainly composed of a CPU and performs a motor control by using a internal program in the CPU.
In this electric power steering apparatus, the motor 108 is an important object to be controlled and a rotation angle sensor and a rotation position sensor are mounted to a rotor of the motor 108 to detect actual rotation angle and rotation position which are used for the motor control. At the same time as this, those sensors are monitored whether they are operating properly or not. An example of the motor control of such an electric power steering apparatus will be described by using a disclosure of Japanese Patent Application Laid-open No. 2000-184774.
FIG. 2 is a block diagram of a motor control disclosed in the above official gazette and a basic operation of the motor control is as follows. First, a magnetizing current command value id* and a torque current command value iq* represented by a d axis and a q axis are obtained. Next, current iu, iv, and iw actually passing through a motor M is measured and converted from three phase to two phase to obtain feedback current idf and idq. Deviations of the feedback current idf and the current iqf from the magnetizing current command value id* and the torque current command value iq* are calculated, respectively, and the deviations are input to a proportional integral circuit (PI circuit) to calculate voltage command values Vd*, Vq*. The calculated voltage command values Vd*, Vq* are converted from two phase to three phase to calculate three-phase voltage command values Vu, Vv, Vw. Command values of a PWM control are determined based on the voltage command values Vu, Vv, Vw, and a driving circuit performs a PWM control of the motor M based on the command values.
Here, a rotation angle sensor and a Hall element 216 as a position detecting sensor are mounted to the motor M. An angle θ of the rotor is calculated in an angle detecting circuit 210 based on a signal detected by the rotation angle sensor, Hall sensor signals from the Hall element 216 and the angle θ of the rotor are input, and an abnormality of the rotation angle sensor and an abnormality of the Hall element are detected by an abnormality detection processing circuit 200.
In this abnormality detection processing circuit 200, a detection abnormality of the Hall element 216 and a detection abnormality of the angle θ of the rotor are detected.
With this method of detecting the abnormality of the rotation angle sensor and the abnormality of the Hall element 216 which is the position detecting sensor, only the abnormal condition of the Hall element 216 which is the position detecting sensor is detected, so a rotational direction when the Hall element 216 is operating normally cannot be detected. Moreover, processing takes much time in referring to a table of criteria of judgment for judging whether the sensors are abnormal or normal, because a plurality of conditional statements are used. Moreover, because both the rotation angle sensor and the Hall element 216 are used, an abnormality judging processing becomes complicated.
The present invention has been made with the above-described circumstances in view and it is an object of the invention to provide a control unit for an electric power steering apparatus with which, by using simple position detecting sensors such as the Hall sensors, it is possible to judge an abnormality of rotational direction detection or a rotational direction when the rotational direction detection is normal in a short processing time and it is possible to detect a steering wheel relative steering angle by using information about the obtained rotational direction.